Got answer to this, below is the code -
Dim wbCurrent As Workbook
Dim wsCurrent As Worksheet
Dim nLastCol, i, j, k As Integer
Set wbCurrent = ActiveWorkbook
Set wsCurrent = wbCurrent.ActiveSheet
nLastCol = wsCurrent.Cells.Find("*", LookIn:=xlValues, SearchOrder:=xlByColumns, SearchDirection:=xlPrevious).Column
j = 0
For i = nLastCol To 1 Step -1
j = j + 1
' k = InStr(1, wsCurrent.Cells(1, i).Value, "Sweep TID", vbTextCompare) > 0
If InStr(1, wsCurrent.Cells(1, i).Value, "unitid", vbTextCompare) = 0 Then
wsCurrent.Cells(1, i).Value = "unitid_" & j
End If
If InStr(1, wsCurrent.Cells(1, i).Value, "UnitName", vbTextCompare) > 0 _
Then
wsCurrent.Cells(1, i).Value = "UnitName_" & j
End If
Next i
The above code identifies the last column with the data in it and uses it in loop